IDocument: Make mimeType a value member

Change-Id: I2e90ccf0a45ae8d00bcd00ec77fe0d9776f2f119
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/qbsprojectmanager/qbsprojectfile.cpp

@@ -39,6 +39,7 @@ QbsProjectFile::QbsProjectFile(QbsProject *parent, QString fileName) : Core::IDo
     m_project(parent)
 {
     setId("Qbs.ProjectFile");
+    setMimeType(QLatin1String(Constants::MIME_TYPE));
     setFilePath(fileName);
 }
 
@@ -65,11 +66,6 @@ QString QbsProjectFile::suggestedFileName() const
     return QString();
 }
 
-QString QbsProjectFile::mimeType() const
-{
-    return QLatin1String(Constants::MIME_TYPE);
-}
-
 bool QbsProjectFile::isModified() const
 {
     return false;